1. The Field of the Invention
The present invention is in the field of fire retardant and heat resistant yarns and fabrics, felts, and other fibrous blends. More particularly, the present invention is in the field of fibrous blends which include oxidized polyacrylonitrile and one or more strengthening fibers and which yield yarns and fabrics having greatly increased LOI and TPP, while maintaining good strength, higher softness and other performance criteria.
2. The Relevant Technology
Fire retardant clothing is widely used to protect persons who are exposed to fire, particularly suddenly occurring and fast burning conflagrations. These include persons in diverse fields, such as race car drivers, military personnel and fire fighters, each of which may be exposed to deadly fires and extremely dangerous incendiary conditions without notice. For such persons, the primary line of defense against severe bums and even death is the protective clothing worn over some or all of the body.
Even though fire retardant clothing presently exists, such clothing is not always adequate to compensate for the risk of severe burns, or even death. Due to the limitations in fire retardance and heat resistance of present state of the art of fire retardant fabrics, numerous layers are typically worn, often comprising different fibrous compositions to impart a variety of different properties for each layer.
In view of the limitations of presently available fire retardant clothing, there has been a long-felt need to find improved yarns, fabrics, felts, and other fibrous blends having better fire retardant properties, higher heat resistance, lower heat transference, improved durability when exposed to constant heat or bursts of high heat, together with adequate strength and abrasion resistance, improved softness, better breathability, improved moisture regain, increased flexibility and comfort, and other performance criteria. Two useful measurements of flame retardance and heat resistance are the Limiting Oxygen Index (LOI) and the Thermal Protective Performance (TPP), which will be defined more filly below.
A wide variety of different fibers and fibrous blends have been used in the manufacture of fire and heat resistant yarns and fabrics. Fire retardance, heat resistance, strength and abrasion resistance all play an important role in the selection of fibers. However, it is difficult to satisfy all of the foregoing desired properties. For example, there is often a compromise between fire retardance and heat resistance, on the one hand, and strength and abrasion resistance, on the other.
Conventional fire retardant fabrics on the market typically rate very high in one, or perhaps two, of the foregoing desired properties. Nevertheless, until now, no one single fiber, fibrous blend or fabric was able to rate high in all, or even most, of the foregoing criteria. For example, the industry standard is currently exemplified by Nomex, which is a proprietary fabric comprising an m-aramid sold by DuPont. When exposed to temperatures of approximately 600.degree. F. and higher, a fabric consisting of Nomex starts to burn, begins to shrink while charring, then cracks and decomposes. This all occurs in about ten seconds.
Whereas Nomex may provide protection to the wearer from burns for approximately ten seconds, which in many cases may be enough time to extinguish the fire or otherwise remove the heat from the wearer's clothing, Nomex nevertheless becomes almost completely worthless as a protective shield after 10 seconds of being exposed to heat at or above 600.degree. F. Once the fabric has charred, cracked and begun to decompose, large holes will typically open up rough which flames and heat can pass, thus burning, or even charring, the naked skin of the person wearing the fabric. Ironically, it is the charring process of the fabric itself that is believed to give the wearer increased thermal protection.
Another flame retardant fabric known in the art is Kevlar, which is a p-aramid material. Whereas Kevlar is adequate in many applications, being durable in abrasion and having high tensile strength, it is relatively stiff, and uncomfortable to wear. In addition, while being superior to many known fibers, it has only modestly high LOI, TPP and continuous operating temperature ratings. Whereas is it self-extinguishing, it nevertheless combusts when exposed to a flame.
In many cases, the fire retardant properties of certain flammable fabrics such as cotton, polyester, rayon, and nylon, have been enhanced by adding a fire retardant finish to the fabric. While this may have the effect of temporarily increasing the flame retardant and heat resistant properties of a given fabric, such fire retardant finishes are not permanent. Exposure of the treated fabric to UV radiation over time, such as being exposed to sun light, as well as routine laundering of the fabric, can cause a reduction in the fire retardant properties of the garment. Not only will a treated garment have reduced fire retardance and heat resistance as the fire retardant finish becomes less effective, but the user may then have a false sense of security, thus unknowingly exposing himself to increased risk of burns. In fact, there may be no objective way to determine, short of being caught in a fiery conflagration or otherwise damaging the garment, whether a treated garment still possesses a high enough level of fire retardance to meet the risks to which the wearer may be exposed.
Accordingly, it would be an advancement in the art to provide improved fire retardant and heat resistant yarns, fabrics, felts and other fibrous blends which were able to satisfy most, if not all, of the desired performance criteria.
In particular, it would be a tremendous improvement in the art to provide improved fibrous blends that yielded fire and flame retardant yarns, fabrics, felts and other fibrous blends that were able to satisfy a wider range of performance criteria compared to conventional fire retardant fabrics.
It would be an additional advancement in the art to provide fire retardant yarns, fabrics, felts and other fibrous blends that had higher continuous operating temperatures, higher LOI and TPP ratings, and improved resistance to heat transfer, while having adequate strength, including tensile strength and abrasion resistance, as well as a softer, more flexible and comfortable feel when known against a person's skin compared to conventional fire retardant fabrics.
Such fire retardant yarns, fabrics, felts and other fibrous blends are disclosed and claimed herein.